The invention is generally related to the field of ion implanters for semiconductor fabrication and more specifically to ARC chambers in ion implanters.
In semiconductor processing, various regions of a semiconductor wafer are modified by implanting dopants, such as boron, phosphorus, arsenic, antimony and the like, into the body of the wafer to produce regions having varying conductivity (e.g., source and drain regions, channel adjusts, etc.). As the density of the semiconductor devices increases, stricter control of the areas to be implanted is required. Thus, ion implanters have been developed to accurately implant dopants into small areas.
In an ion implanter, an ion beam of the desired chemical species is generated by means of a current applied to a filament within an ion source chamber. One of the more common types of source is the Freeman source. In the Freeman source, the filament, or cathode, is a straight rod that can be made of tungsten or tungsten alloy, or other known source material such as iridium, that is passed into an arc chamber whose walls are the anode. The ions are extracted through an aperture in the arc chamber by means of a potential between the source chamber, which is positive, and extraction means. The size and intensity of the generated ion beam can be tailored by system design and operating conditions; for example, the current applied to the filament can be varied to regulate the intensity of the ion beam emitted from the ion source chamber.
A top view of a prior art arc chamber 10 is shown in FIG. 1. Arc Chamber 10 typically comprises molybdenum or tungsten and is fitted with an exit aperture 12 and with means 14 for feeding in the desired gaseous ion precursors for the desired ions. Arc chamber 10 includes a filament end 18 for inserting a filament and a repeller end 16. When power is fed to the filament, the filament temperature increases until it emits electrons that bombard the precursor gas molecules, breaking up the gas molecules so that a plasma is formed containing the electrons and various ions. The ions are emitted from the arc chamber 10 through the exit aperture 12 and selectively passed to the target.
The inner contour of arc chamber 10 is carefully designed and must be extremely accurate for proper operation. Unfortunately, the inner surface of the arc chamber 10 is damaged over time by the plasma. The surface of the arc chamber wears away. Sputtered deposits of tungsten or molybdenum from the chamber walls create an inefficiency in the extraction of positively charged ions from the source ACR chamber. After a time of 3-6 months, the arc chamber becomes unusable and must be replaced. Replacement ARC chambers cost on the order of $3000-$6000 and up. Thus, there is a desire to minimize this cost.
The invention is an arc chamber for an ion implanter. The arc chamber comprises a liner that extends the life of the arc chamber. When the liner wears out it is replaced at a significantly reduced cost compared to replacing the entire arc chamber.
An advantage of the invention is providing an arc chamber with an extended life versus the prior art.